Page:Popular Science Monthly Volume 27.djvu/500

482 produces hairs. Half a dozen are early spring plants which flower before the ants are roused from their winter sleep; about the same number are minute ground-plants to which hairs could be no protection; three or four are night flowers; there still remain a few to be accounted for, which would have to be considered individually, but probably the evidence is sufficiently complete to justify the general inference.

Lastly, I must not omit to mention the hairs which have a glandular character.

The next point to which I would call attention is the remarkable manner in which certain forms repeat themselves. In some cases, there seems much reason to suppose that one plant derives a substantial advantage from resembling another. For instance, Chrysanthemum inodorum, the scentless mayweed, very closely resembles the camomile in leaves, flowers, and general habit. The latter species, however, has a strong, bitter taste, which probably serves as a protection to it, and of which also, perhaps, the scentless mayweed may share the advantage. These two species, however, are nearly allied to one another, and I prefer, therefore, to take as an example of mimicry the stinging-nettle (Urtica) and the common dead-nettle (Lamium album). These two species belong to totally different families; the flowers are altogether unlike, but the general habit and the form of the leaves are extremely similar.

How close the similarity is may be seen by the illustration (Fig. 21), taken from an excellent photograph made for me by Mr. Harman, of Bromley. The plants on the right are true stinging-nettles; those on the left are the white dead-nettle, one of which is in flower. So close was the resemblance that, after getting the photograph, I went back to the spot on which they were growing to assure myself that there was no mistake. It can not be doubted that the true nettle is protected by its power of stinging; and, that being so, it is scarcely less clear that the dead-nettle must be protected by its likeness to the other. Moreover, though I was fortunate in lighting on so good an illustration as that shown in the figure just when I had the opportunity of photographing it, still every one must have observed that the two species are very commonly found growing together. Assuming that the ancestor of the dead-nettle had leaves possessing a faint resemblance to those of the true nettle, those in which the likeness was greatest would have the best chance of survival,